Project 4 will exploit the unique advantages of isolated circuits generated by central neuron grafting strategies to study the cellular neurobiology of aging. The project will examine age-related changes in central noradrenergic and cholinergic circuits, using single and double in oculo grafts. Changes in presynaptic and postsynaptic mechanisms in central noradrenergic circuits will be evaluated using in vivo chronoamperometric and electrophysiological approaches; correlative morphological and biochemical measurements will also be carried out. We will focus on locus coeruleus, cerebellum and hippocampus. Intrinsic vs extrinsic determinants of age related alterations will be tested by examining 1) heterochronic syngeneic grafts, 2) allogenic grafts and 3) grafts to calorically restricted hosts. Double and triple grafts of locus coeruleus with central and peripheral targets will be used to study age-related changes in plasticity of central noradrenergic neurons. Effects of putative trophic factors, such as NT-3, on such plasticity will also be examined. The actions of another putative trophic factor, GDNF, will be studied on cholinergic single and double grafts of medial septal nucleus and hippocampus. Finally, hypotheses relating to the toxic effects of free radicals, and possible reversal of such toxic effects by free radical scavengers, will be tested by exposing grafts to normabaric oxygenation and then injecting spin-trap compounds systemically or in oculo.